Can Vitamin C prevent the common cold?

Posted 1 March 2015 12:00 AM by Dr Sarah Brewer

An interesting case study, just published, reports that high dose vitamin C helped clear a persistent parvovirus B19 infection in a 54-year old woman whose chronic joint pains had lasted six months without responding to standard treatments (i). Her anti-inflammatory drugs were stopped and a French hospital for infectious diseases prescribed high doses of oral vitamin C (10g per day for 10 days) ‘as suggested in other viral illnesses’. After five days, she experienced a dramatic decrease in symptoms and after three weeks, tests showed her active viral infection had cleared.

While the timing could have been coincidental, the doctors involved believe the high doses of vitamin C were effective. This got me thinking about the effectiveness of vitamin C in preventing and treating the common cold and I took another look at the evidence.

Common cold

The antiviral action of vitamin C results from suppressing the activation of viral genes. Put simply, viruses cannot replicate inside human cells if high levels of vitamin C (ascorbic acid) are present. Researchers also believe the powerful antioxidant action of vitamin C mops up inflammatory chemicals produced during a viral infection, to improve symptoms and hasten healing if a cold develops (ii).

Early studies involving school children and students (iii) found that taking vitamin C reduced the risk of catching a cold by as much as 30%. Men doing heavy physical exercise are particularly prone to respiratory infections, and taking 600mg to 1g vitamin C per day was found to half the risk of cold symptoms for military troops under training, as well as for participants in a 90 km running race (iv).

In people with asthma, cold viruses are a well-known trigger for attacks. At least two studies showed that vitamin C supplements decreased the occurrence of respiratory infection-induced asthma attacks by as much as 78% - partly through the antiviral action, but also through an ability to ‘normalise’ airway sensitivity (v).

The most recent Cochrane review into vitamin C and colds included data from 30 trials involving over 11,300 people. This found a consistent treatment benefit with a reduction in the duration of a cold of 8% in adults and, in children taking 1g to 2g per day, a reduction of 18%. The severity of cold symptoms was also reduced (vi). Although this review found no evidence to support an effect in preventing colds, this was probably because doses higher than those usually taken are needed (vii).

So what’s my best advice? I take vitamin C 500mg daily (in chewable form) and hardly ever develop a cold. If one does rear its head, I up my vitamin C dose, reach for my Pelargonium tablets and know that within 24 hours these symptoms will be a distant memory!